Duane Retraction Syndrome Type 2 via the CHN1 Gene
Summary and Pricing 
Test Method
Exome Sequencing with CNV Detection
| Test Code | Test Copy Genes | Test CPT Code | Gene CPT Codes Copy CPT Code | Base Price | |
|---|---|---|---|---|---|
| 8197 | CHN1 | 81479 | 81479,81479 | $990 | Order Options and Pricing |
Pricing Comments
Our favored testing approach is exome based NextGen sequencing with CNV analysis. This will allow cost effective reflexing to PGxome or other exome based tests. However, if full gene Sanger sequencing is desired for STAT turnaround time, insurance, or other reasons, please see link below for Test Code, pricing, and turnaround time information.
An additional 25% charge will be applied to STAT orders. STAT orders are prioritized throughout the testing process.
Click here for costs to reflex to whole PGxome (if original test is on PGxome Sequencing platform).
Click here for costs to reflex to whole PGnome (if original test is on PGnome Sequencing platform).
The Sanger Sequencing method for this test is NY State approved.
For Sanger Sequencing click here.Turnaround Time
3 weeks on average for standard orders or 2 weeks on average for STAT orders.
Please note: Once the testing process begins, an Estimated Report Date (ERD) range will be displayed in the portal. This is the most accurate prediction of when your report will be complete and may differ from the average TAT published on our website. About 85% of our tests will be reported within or before the ERD range. We will notify you of significant delays or holds which will impact the ERD. Learn more about turnaround times here.
Targeted Testing
For ordering sequencing of targeted known variants, go to our Targeted Variants page.
Clinical Features and Genetics
Clinical Features
Duane retraction syndrome (DRS) is a congenital ocular disorder characterized by restricted horizontal eye movement with retraction of the globe and narrowing of the lid fissure in attempted adduction (monocular rotation of the eye toward the nose). DRS accounts for 1- 5% of all strabismus sporadic cases and 10% of the familial cases. DRS untreated in childhood can result in amblyopia and loss of binocular vision (Miyake et al. 2010; DeRespinis et al. 1993)
Genetics
Pathogenic variants in CHN1 are involved in autosomal dominant Duane's retraction syndrome (DRS) (Chan et al. 2011). CHN1 encodes alpha2-chimaerin, a Rac guanosine triphosphatase-activating protein (RacGAP). Animal studies have shown that causative variants in this gene are gain-of-function variants that interfere with normal innervation of target eye muscles by oculomotor axons in chick embryos (Miyake et al. 2008). So far only missense variants (~10) have shown to be causative for DRS (Human Gene Mutation Database).
Clinical Sensitivity - Sequencing with CNV PGxome
Miyake et al. reported a 35% detection rate of CHN1 pathogenic variants in familial Duane retraction syndrome (Miyake et al. 2008). However, another study tested 140 sporadic DRS cases and did not detect any pathogenic variants in CHN1 (Miyake et al. 2010).
Testing Strategy
This test provides full coverage of all coding exons of the CHN1 gene plus 10 bases of flanking noncoding DNA in all available transcripts along with other non-coding regions in which pathogenic variants have been identified at PreventionGenetics or reported elsewhere. We define full coverage as >20X NGS reads or Sanger sequencing. PGnome panels typically provide slightly increased coverage over the PGxome equivalent. PGnome sequencing panels have the added benefit of additional analysis and reporting of deep intronic regions (where applicable).
Dependent on the sequencing backbone selected for this testing, discounted reflex testing to any other similar backbone-based test is available (i.e., PGxome panel to whole PGxome; PGnome panel to whole PGnome).
Indications for Test
Patients with congenital abnormalities of eye movements are candidates (Oystreck et al. 2011; http://novel.utah.edu/diseases/rare-registry/view/Unusual_Congenital_Ocular_Motility_Disorders).
Patients with congenital abnormalities of eye movements are candidates (Oystreck et al. 2011; http://novel.utah.edu/diseases/rare-registry/view/Unusual_Congenital_Ocular_Motility_Disorders).
Gene
| Official Gene Symbol | OMIM ID |
|---|---|
| CHN1 | 118423 |
| Inheritance | Abbreviation |
|---|---|
| Autosomal Dominant | AD |
| Autosomal Recessive | AR |
| X-Linked | XL |
| Mitochondrial | MT |
Disease
| Name | Inheritance | OMIM ID |
|---|---|---|
| Duane Syndrome Type 2 | AD | 604356 |
Citations
- Chan W.M. et al. 2011. Archives of Ophthalmology. 129: 649-52. PubMed ID: 21555619
- DeRespinis P.A. et al. 1993. Surv Ophthalmol. 38(3):257-88. PubMed ID: 8310396
- Human Gene Mutation Database (Bio-base).
- Miyake N. et al. 2008. Science. 321: 839-43. PubMed ID: 18653847
- Miyake N. et al. 2010. American Journal of Medical Genetics. Part A. 152A: 215-7. PubMed ID: 20034095
- Oystreck D.T. et al. 2011. Journal of neuro-ophthalmology. 31: 69-77. PubMed ID: 21317732
Ordering/Specimens
Ordering Options
We offer several options when ordering sequencing tests. For more information on these options, see our Ordering Instructions page. To view available options, click on the Order Options button within the test description.
myPrevent - Online Ordering
- The test can be added to your online orders in the Summary and Pricing section.
- Once the test has been added log in to myPrevent to fill out an online requisition form.
- PGnome sequencing panels can be ordered via the myPrevent portal only at this time.
Requisition Form
- A completed requisition form must accompany all specimens.
- Billing information along with specimen and shipping instructions are within the requisition form.
- All testing must be ordered by a qualified healthcare provider.
For Requisition Forms, visit our Forms page
If ordering a Duo or Trio test, the proband and all comparator samples are required to initiate testing. If we do not receive all required samples for the test ordered within 21 days, we will convert the order to the most effective testing strategy with the samples available. Prior authorization and/or billing in place may be impacted by a change in test code.
Specimen Types
Specimen Requirements and Shipping Details
PGxome (Exome) Sequencing Panel
PGnome (Genome) Sequencing Panel
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ORDER OPTIONS
View Ordering Instructions1) Select Test Type
2) Select Additional Test Options
No Additional Test Options are available for this test.